1. Field of the Invention
The invention relates to a wear protection cap for a bit holder arrangement.
2. Description of the Prior Art
DE 10 2009 059 188 A1 (U.S. Pat. No. 8,746,806) discloses a bit holder arrangement. The latter encompasses a base part and a bit holder. The base part can be welded onto the outer surface of a tubular milling drum. The bit holder can then be replaceably fastened on the base part. A plurality of bit holder arrangements are secured on the surface of the tubular milling drum. They are preferably placed with respect to one another so that the base parts form a clearing and loading helix. A bit, preferably a rotatable round shank bit, can be replaceably received in the bit holder. The bit holder arrangements known from DE 10 2009 059 188 A1 are used in mining, preferably in open-cast mining. During processing use, the bits cut into the substrate that is to be removed, and detach material. The removed material flows off laterally past the bit and the bit holder and then arrives in the region of the base parts that form the clearing and loading helix. The base parts then therefore transport the removed material into the region of the center of the tubular milling drum, where it is then delivered to a loading belt.
Depending on its nature, the material produces different degrees of wear as a result of abrasion processes. Whereas rather less wear occurs with softer formations, such as coal, considerable wear can take place with materials containing iron ore. The bits are subjected to particularly severe wear and must therefore be changed at regular intervals. The bit holders, on the other hand, are designed to survive over the service life of a plurality of bits. The base part, constituting the most expensive unit of the bit holder arrangement, is intended to offer a particularly long service life. In order to delay cost-intensive replacement of the base parts, it is known from the existing art to weld facing plates, in the form of steel sheets, onto particularly threatened regions of the base parts. This procedure, upon initial population of a milling drum, is time-intensive, since a plurality of delicate components must be handled, but a longer service life can thereby be obtained. It has been found, however, that the sheets are subjected to increased wear especially in the region of the weld seams. The thermal effect resulting from the welding operation causes a reduction in the strength of the steel sheet in the region adjacent to the weld seam. Greater wear accordingly occurs here as compared with the other surface regions. The facing plates accordingly detach in uncontrolled fashion from the base part after a certain service time as a result of component failures. The use of additional welding material is time- and cost-intensive and thus increases part complexity.
Further wear protection systems are also known from the existing art. Hardface welds, for example, are applied directly onto bit holders or base parts of the bit holder arrangement. Effective wear protection can thereby be achieved, but the outlay for applying the welds is considerable.